STARFIRE-2: Can We Detect the Global Redshifted 21 cm Signal from the Cosmic Dawn in Earth Orbit?

Abstract

Detecting the redshifted global 21 cm signal from the cosmic dawn remains a major challenge due to strong terrestrial radio-frequency interference (RFI), particularly dominated by frequency modulation (FM) transmissions in the 88–110 MHz range. While observations from the radio-quiet lunar farside are ideal, Earth orbit offers an intermediate and simpler alternative that may mitigate several limitations of ground-based experiments. We assess the feasibility of detecting the global 21 cm signal from Earth orbit by quantifying FM-based RFI at different altitudes and orbital configurations. We present Simulation of TerrestriAl Radio Frequency Interference in oRbits around Earth—2 (STARFIRE-2), an algorithm that estimates FM transmitter–based RFI intercepted by radiometers in orbit. The model constructs a global FM transmitter database and compensates for incomplete data using statistical methods. Using PRATUSH as the reference experiment, we simulate a range of orbital scenarios to identify configurations that minimize RFI and optimize sensitivity for global 21 cm detection. The algorithm can also be adapted for other experiments. Simulations indicate that conducting such an experiment from Earth orbit is feasible for a thermal noise limited instrument placed in a low Earth, near-polar orbit. Mock sky observations further demonstrate that most theoretically plausible cosmic dawn 21 cm signals can be recovered with high confidence under these optimized orbital conditions.